- Email: [email protected]
Can cutaneous vibration affect pain development? Testing the efficacy of a vibrating belt applied intermittently to the low back region during prolonged standing
International Journal of Industrial Ergonomics 66 (2018) 95e100
Contents lists available at ScienceDirect
International Journal of Industrial Ergonomics journal homepage: www.elsevier.com/locate/ergon
Can cutaneous vibration affect pain development? Testing the efficacy of a vibrating belt applied intermittently to the low back region during prolonged standing Analyssa Cardenas a, Diane E. Gregory b, * a b
Department of Kinesiology, University of Waterloo, Waterloo, Canada Department of Kinesiology & Physical Education/Health Sciences, Wilfrid Laurier University, Waterloo, Canada
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 July 2017 Received in revised form 11 January 2018 Accepted 23 January 2018
Standing-induced low back pain (LBP) is becoming more common in the workplace and has been shown to develop in periods of as short as 2 h. The purpose of this study was to determine if vibration, an increasingly popular method of pain relief, applied intermittently (every 15 min) directly to the low back could alleviate pain developed during a 2-h period of standing. Two separate collection days were conducted (order randomized). During the control day, no vibration was applied during the 2 h of standing; on an experimental day, vibration was applied via a vibration belt in 3-min durations every 15 min for 2 h. During both data collections, perceived LBP was collected via a visual analogue scale every 15 min; on the experimental day LBP was collected just prior to and following each vibration bout. Force plate data were also collected to determine centre of pressure changed over time. LBP significantly increased over time on both collection days; however, on the vibration day LBP reported just prior to each vibration bout was significantly higher than that immediately following, suggesting a temporary relief of pain. However, this relief of pain was not sustained as the level of perceived LBP at the end of the 2 h on the control day was not significantly different from that on the vibration day. Decreases in anterior-posterior and medial-lateral centre of pressure movement were also observed during each bout of vibration compared to during the control day. In conclusion, while intermittent vibration applied to the low back appears to relieve LBP developed during standing, this relief is temporary. © 2018 Published by Elsevier B.V.
Keywords: Vibration Massage belt Centre of pressure Visual analogue scale Low back pain
1. Introduction Low back pain (LBP) continues to be a prevalent cause of missed work and disability among the developed world (Hoy et al., 2014; et al., 2012). Typically, manual material handing is thought Balague to be the major contributor of work-related LBP; however recent evidence has shown that sedentary tasks can have negative health impacts (Thorp et al., 2011; Tremblay et al., 2010) and can result in LBP in the case of prolonged sitting (Garcia et al., 2014; Womersley , 1999) and standing (Coenen & May 2006; Videman and Battie et al., 2017; Waters and Dick, 2015; Janwantanakul et al., 2011; Mohseni-Bandpei et al., 2011; Nelson-Wong and Callaghan, 2010a; Gregory and Callaghan, 2008; Andersen et al., 2007; Roelen et al.,
* Corresponding author. Department of Kinesiology & Physical Education, Department of Health Sciences, Wilfrid Laurier University, 75 University Ave West, Waterloo, Ontario, N2L 3C5, Canada. E-mail address: [email protected] (D.E. Gregory). https://doi.org/10.1016/j.ergon.2018.01.015 0169-8141/© 2018 Published by Elsevier B.V.
2008). While a significant number of ergonomic interventions, primarily related to chair design, have been developed and examined for sitting, less focus has been placed on prolonged standing. The efficacy of a variety of ergonomic interventions including floor type and mats (Aghazadeh et al., 2015; Waters and Dick, 2015), intermittent spinal flexion (Stewart and Gregory, 2016), and standing on a sloped surface (Fewster et al., 2017; Nelson-Wong and Callaghan, 2010a) have been examined, however LBP still remains prevalent, suggesting a need for alternative pain mitigation strategies. Recently, vibration, administered through whole body vibration (typically by standing on a vibrating platform; Perraton et al., 2011) or through the use of a massage device (Imtiyaz et al., 2014), has become more common for musculoskeletal pain management (Cochrane, 2017; Zafar et al., 2015; Lau and Nosaka, 2011). One possible hypothesis is that vibration inhibits nerve fibres responsible for transmitting pain (Magee et al., 2007). This hypothesis, termed the gate control theory of pain (Melzack and Wall, 1965),
96
A. Cardenas, D.E. Gregory / International Journal of Industrial Ergonomics 66 (2018) 95e100
suggests that vibration stimulates the same large diameter peripheral nerve fibres that are activated in response to pain (Melzack and Wall, 1965; Cochrane, 2011; Nanitsos et al., 2009), thereby preventing transmission of pain-related information. Since prolonged standing has been shown to result in significant levels of LBP in previously asymptomatic populations after as little as 2 h (Stewart and Gregory, 2016; Nelson-Wong and Callaghan, 2010b; Nelson-Wong et al., 2010; Gregory and Callaghan, 2008), it is possible that exposure to low back vibration may help alleviate or reduce LBP in such individuals, providing an alternative mechanism of pain relief. Further, given the increased popularity of sit-stand workstations, the prevalence of prolonged standing is also increasing among many occupations. Therefore, the primary purpose of this study was to determine if intermittent bouts of vibration applied to the low back region through a vibrating massage belt is effective at reducing the level of LBP developed during a 2-h period of standing. The secondary purpose of this study was to determine if vibration alters movement of the centre of pressure (CoP) at the feet during prolonged standing. It was hypothesized that 1) vibration would significantly reduce LBP developed during prolonged standing, and 2) vibration would significantly reduce CoP movement at the feet. 2. Methods
vibration periods). The order of the control and experimental days were randomized and each collection was completed at approximately the same time of day one week apart.
2.3. Data collection Ratings of each of perceived LBP, leg/feet pain, and overall pain were recorded using 100 mm visual analogue scales (VAS) with the anchors of no pain (0 mm) and worst pain imaginable (100 mm). On the control day, ratings of perceived LBP were collected every 15 min during the 2-h standing protocol. On the experimental day, two ratings of perceived LBP were collected every 15 min; one just prior to the start of the 3-min vibration and one immediately following the vibration for a total of 16 ratings (Fig. 1). Participants also had the opportunity, if they wished, to indicate on the same form if they were feeling any of the following pain-related symptoms in their backs: tiredness, soreness, numbness, sharp, dull, tingling, distributed, and localized (de Looze et al., 2003). Force plate data were recorded on both the control and experimental collection days. On the control day, 3-min periods were recorded just prior to each pain rating. On the experimental day, 3min periods were recorded just prior to each vibration application (VibOFF) and during each 3-min vibration period (VibON); Fig. 1. Force plate data were sampled at 128 Hz.
2.1. Participants A sample of 15 healthy participants (8 female; 7 male) were recruited from a university population (mean (standard deviation) age ¼ 21 years (1.0); height ¼ 1.67 m (0.09); mass ¼ 62.6 kg (9.6)). Participants were required to be free of LPB for the previous 12 months and not have suffered from any neurological conditions that could affect balance. Participants were asked to come to the laboratory for testing on two separate days, one week apart, to perform a 2-h standing protocol. 2.2. Study protocol On the first visit, participants were briefed on the study protocol, given the opportunity to familiarize themselves with the vibration belt device, and asked to review and sign a consent form for the study which had been approved by the University human ethics board. Participants were then instructed to stand for a 2 h period (on a 60 90 cm force plate; Bertec, Columbus, Ohio) while performing tasks resembling jobs that often require prolonged periods of standing: small object assembly, currency sorting, barcode scanning, and typing (each performed for 30 min). The desk on which these tasks were performed was set for each participant such that the elbow angle was slightly greater than 90 when the forearms rested on the table. This desk height was the same on both collection days. Leaning on the desk was not permitted, but the forearms were allowed to rest while performing the tasks. Further, individuals were instructed to keep their feet on the force plate but they could shift their weight and/or move their feet within the area of the force plate throughout the collection. Personal athletic footwear was worn by each participant. Prior to both collection periods, each participant was fitted with a vibrating massage belt (Zewa Spa Buddy; factory setting vibration ¼ 53 Hz) around his/her waist such that the vibration was applied to the lower back and sacrum region. On the control day, the belt was worn for the entire duration of the study, but it was turned off the entire time; on the experimental day, vibration was applied via the belt for 3-min durations every 15 min (total of 8
2.4. Data analysis Perceived pain was quantified by measuring the distance from the origin (0 mm) to the participant's mark on the 100 mm VAS; the greater the distance measured, the more intense the pain. Participants were subsequently classified as either LBP developers (reached a low back VAS score of at least 10 mm at any point during the control day standing period) or non-low back pain developers (never reached 10 mm during the control day standing period), as 10 mm has been previously considered a clinically significant level of LBP (Gallagher et al., 2011; Nelson-Wong and Callaghan, 2010a; Hagan and Albert, 1999). Force plate data were low-pass filtered at 6 Hz using a second order dual-pass Butterworth filter and CoP at the feet was determined. Variables of interest, which were determined for each 3min force plate collection period, included anterior-posterior (AP) CoP range (CoPAP), medio-lateral (ML) CoP range (CoPML), AP root mean square (RMS) (CoPAP_RMS), ML RMS (CoPML_RMS), AP velocity range (VelocityAP), ML velocity range (VelocityML), AP velocity RMS (VelocityAP_RMS), ML velocity RMS (VelocityML_RMS), and cumulative path length (CPL).
2.5. Statistical analysis Three-way analysis of variance (ANOVA) tests and Tukey posthoc tests (Statistical Analysis System (SAS) software) were used to examine the effect of vibration exposure (2 levels: control/experimental day (pre-vibration time points)), time point (8 levels; 15 min intervals; the pre vibration VAS scores on the experimental day were compared with the 15 min interval scores on the control day), and LBP classification (2 levels: yes/no) on VAS scores. A separate three-way ANOVA was conducted on only the experimental day data with the following factors: pre/post vibration, time point, and LBP classification on VAS scores. Similar three-way ANOVA statistical analyses were conducted on the aforementioned CoP variables. An alpha level of 0.05 was set as significant.
A. Cardenas, D.E. Gregory / International Journal of Industrial Ergonomics 66 (2018) 95e100
97
Fig. 1. Control and experimental day protocol timeline. Time is shown in 15 min intervals over the 2-h collection. Solid grey regions indicate when force plate data were collected to calculate CoP changes and diagonal line regions indicate when vibration was applied. All regions represent 3 min of time. Solid black vertical lines indicate when VAS pain ratings were recorded.
3. Results 3.1. Perceived pain Of the 15 participants, seven were classified as LBP developers (average (standard error) VAS of 26.3 mm (4.6) at the 2-h mark) and eight were classified as non-LBP developers (average VAS of 2.3 mm (0.9) at the 2-h mark). 3.1.1. Perceived pain over time On both the control day and the experimental day, ratings of perceived pain in the low back (p ¼ 0.0001), feet and legs (p ¼ 0.0001) and overall pain (p ¼ 0.0001) increased over time (Fig. 2). Further, in addition to greater LBP, those who were classified as LBP developers reported more feet/leg and overall pain compared to non-LBP developers as indicated by significant interactions between classification and time point (p ¼ 0.009 for feet/ legs and p ¼ 0.002 for overall pain). 3.1.2. Perceived pain developed on control day versus experimental day and pre versus post vibration Collapsed across time point and LBP classification, no differences in perceived pain were observed between the control day and the vibration day (specifically at time points just before each vibration exposure) (p ¼ 0.69, 0.50, 0.31 for low back, legs/feet, and overall pain, respectively). However, on the experimental day, collapsed across time and LBP classification, significant differences in perceived LBP were
observed immediately prior to and immediately after each 3-min bout of vibration exposure (p ¼ 0.039). Specifically, average LBP before vibration exposure was 9.11 mm (3.42) and 7.56 mm (2.99) immediately after. At the 75 and 90-min marks, the vibration exposure, on average, reduced perceived LBP from an above clinical level (>10 mm) to below (Fig. 3); however this sub-clinical level of LBP did not continue for the remainder of the 2 h. Further, this decrease was not different over time as no interaction with time point was observed (p ¼ 0.20). No main effect of vibration exposure was observed for perceived pain in the feet/legs (p ¼ 0.66) or in overall pain (p ¼ 0.20). A significant interaction between pre/post vibration and time point was observed for pain in the feet/legs (p ¼ 0.028; Fig. 4) such that at the 75 and 105 min marks, post vibration perceived pain was actually higher than pre vibration (Fig. 4). 3.2. Centre of pressure (CoP) 3.2.1. CoP over time Regardless of vibration exposure (i.e. control versus experimental day), a number of CoP variables were significantly affected by time such that, in general, CoP variables tended to increase, albeit minimally, over time (Fig. 5). Specifically, the following variables were affected by time point: range in the CoPAP (p ¼ 0.023), range in CoPML (p ¼ 0.012), CoPAP_RMS (p ¼ 0.003), CoPML_RMS (p ¼ 0.0007), and CPL (p ¼ 0.026). One additional variable (range of the CoPML velocity) was not affected by time as a main effect; however a significant interaction between time point and vibration exposure was observed (p ¼ 0.023) such that VelocityML tended to vary substantially over time on both the control day and the experimental day.
20 18
Low Back Pain (mm)
16 14 12
10
Pre
8
Post
6
Control
4 2 0
Fig. 2. Average (standard error) ratings of perceived low back, feet/legs, and overall pain over time collapsed across day (control and experimental) and LBP classification. Bars within the same category (i.e. LBP; feet/legs; overall) with the same letter are not significantly different from one another (p > 0.05). For example, for the black bars, which represent overall pain, the magnitude at 15 min is not significantly different from the magnitude at 30 or 45 min as all 3 bars have at least one common letter above (in this case “A”). However, at 60 min, there is no “A” above the black overall pain bar, and therefore it is significantly different from 15 min, but not different from 30 or 45 min because each bar shares the letter “B”.
15
30
45
60
75
90
105
120
Time (mins) Fig. 3. Average (standard error) ratings of perceived low back pain on the control day as well as pre and post vibration exposure on the experimental day (data collapsed across LBP classification). Collapsed across time, Pre versus Post LBP levels were significantly different (p ¼ 0.039); no significant interaction between pre/post and time was observed. Effect of time point indicated previously in Fig. 2. No significant difference between the pre vibration LBP scores and the control day LBP scores.
A. Cardenas, D.E. Gregory / International Journal of Industrial Ergonomics 66 (2018) 95e100
a
35
Feet/Leg Pain (mm)
30 25
*
*
20
0.05 Pre
15
Post
10 5 0 15
30
45
60
75
*
0.04
90
105
120
COPML_RMS (m)
98
0.03 0.02 0.01 0
Time (mm)
Control
VibOFF
VibON
b 6
Cumulative Path Length (m)
Fig. 4. Average (standard error) perceived feet/leg pain over time on the experimental day (collapsed across LBP classification). Effect of time point indicated previously in Fig. 2. Significant interaction between time point and pre/post (p ¼ 0.028); asterisks indicate time point where post vibration feet/leg pain scores were higher than pre vibration.
5
Non-LBP developers
*
LBP developers
4 3 2 1 0 Control
Fig. 5. Average (standard error) CoP variables significantly affected by time. For CoPAP, 15- and 30-min differed from 105-min (p ¼ 0.023); for CoPML, 15-min differed from 90min (p ¼ 0.012); for CoPAP_RMS, 15-, 30-, and 45-min differed from 105-min (p ¼ 0.003); for CoPML_RMS, 15-min differed from 75-, 90-, and 105-min; 30-min also differed from 75-min (p ¼ 0.0007); for CPL, 60-min differed from 90-min (p ¼ 0.026). Data collapsed across day (control and experimental) and LBP classification..
3.2.2. CoP during control day versus prior to and immediately following vibration on experimental day In terms of the effect of vibration exposure, two variables (CoPML_RMS and CPL) were significantly affected (Fig. 6). In general, these CoP variables tended to be highest on the control day and lowest on the experimental day when the vibration was on. For CoPML_RMS (p ¼ 0.04), the control day only significantly differed from vibration ON condition. For the CPL, the control day significantly differed from both the vibration ON and vibration OFF conditions (Fig. 6a; p ¼ 0.001). However, only those who were non LBPdevelopers actually showed the drop in CPL on the experimental day; the CPL of the LBP developers did not differ between the control day and the experimental day (indicated by significant interaction between LBP classification and vibration exposure; p ¼ 0.032; Fig. 6b). No other main effects of LBP classification were observed. 4. Discussion Low back pain (LBP) has long been recognized as a significant health issue, particularly in occupations that require prolonged periods of standing (Macfarlane et al., 1997; Xu et al., 1997). With the increase in LBP prevalence in many occupations, there has been a growing interest in the use of vibration, which has been shown to be effective at reducing muscle pain (Cochrane, 2017; Zafar et al., 2015; Lau and Nosaka, 2011). This study demonstrated that low back vibration can offer an immediate relief of LBP over a short period of time, but does not appear to offer long term (over 2 h) positive effects.
VibOFF
VibON
Fig. 6. (a) Average (standard error) CoPML_RMS on the control day and on the experimental day (vibration on and vibration off); collapsed across time point and LBP classification. Only the control and VibON conditions significantly differed from one another (indicated by asterisk). (b) Average (standard error) CPL on the control and experimental day (including when vibration was on and off) for those who developed LBP and those who did not; collapsed across time point. Note that the CPL did not differ between the LBP and non-LBP developers during the VibOFF and VibON conditions, but that on the control day, the CPL was significantly higher for the non-LBP developers compared to non-LBP developers (indicated by asterisk).
Specifically, after 3 min of low back vibration, an immediate relief in LBP was observed. However, this decrease in reported pain was transient because once the vibration was removed, the pain returned by the time the next vibration period was applied (12 min later). Further, LBP reported at the 2-h mark was no different on the experimental day when vibration was applied compared to the control day despite the observed immediate drops in pain reported after each vibration bout, indicating that the temporary relief was not effective at mitigating pain longer term. The observed transient and immediate relief of pain following each bout of vibration can most likely be explained by the gate control theory of pain (Melzack and Wall, 1965). The brain receives information on painful stimuli through the noxious stimulus itself, the modulation of peripheral nerves, and the descending contrl by the central nervous system (Melzack and Wall, 1965). The injury detection threshold of large diameter peripheral nerve fibres (Ab fibres) increases when the nerves are stimulated (Melzack and Wall, 1965). When vibration is applied, the activation of low threshold mechanoreceptors causes the stimulation of these large diameter peripheral nerves (Melzack and Wall, 1965; Cochrane, 2011; Nanitsos et al., 2009). This effectively induces inhibition of the perception of pain by blocking the transmission of information being sent to the central nervous system (Melzack and Wall, 1965). Although the 3 min bouts of low back vibration caused an immediate decrease in pain for a short period of time, it did not eliminate the LBP completely. Average LBP prior to vibration
A. Cardenas, D.E. Gregory / International Journal of Industrial Ergonomics 66 (2018) 95e100
exposure was 9.11 mm and reduced to 7.56 mm immediately following vibration. Interestingly, at the 75 and 90-min mark, of the standing protocol, vibration temporarily reduced LBP to a below clinical level (<10 mm; Gallagher et al., 2011; Nelson-Wong and Callaghan, 2010a; Hagan and Albert, 1999). However, by the 2-h mark, there was no difference in low back pain between the experimental (vibration) day and the control day, indicating that vibration is not effective at long-term pain reduction. It should be noted that, although a significant drop in pain was noted, this drop was only ~2 mm which may not enough to have a notable impact on the individual. Previous research has suggested that a drop in pain €gg et al., 2003). must be at least 8 mm to be considered effective (Ha However, there were two individuals in the study that did report a greater than 8 mm drop in LBP following vibration, suggesting that it may be an effective strategy for some. Though, for both of these individuals, their LBP score at the end of the control day and the vibration day only differed by 1 mm, suggesting that although pain relief was observed immediately following vibration, it was not sustained. Although the vibration offered temporary relief of pain, there is also the possibility of detrimental effects on a long term scale. It is speculated that this vibration, if applied for a longer period of time, may trigger an exaggerated pain response. It has been demonstrated that mechanical vibration of a similar frequency to that in the current study (60e80 Hz) applied to the hind limb of rat resulted in skeletal muscle hyperalgesia (Dina et al., 2010). This hypersensitivity to pain can be explained by a number of different mechanisms. When mechanical vibration is applied, very highfiring nociceptors produce an enhanced and prolonged response to sustained mechanical stimulation (Chen et al., 2010). The vibration lowers the mechanical threshold, suggesting that these nociceptors may contribute to neuropathic muscle pain even after vibration is removed (Chen et al., 2010). Repeated daily applications of brief vibration stimulation have also been shown to prolong hyperalgesia in comparison to no vibration exposure (Kim et al., 2007). Further research needs to be conducted to determine whether repeated intermittent vibration over time will induce a higher sensitivity of pain in the lower back. In addition to increased pain sensitively, prolonged vibration exposure may also disrupt motor control patterns. The use of muscle vibration for prolonged periods of time has been shown to cause a reduction in electrical activity of muscles, motor unit firing rates, and contraction force for both intermittent and sustained maximal voluntary contractions (Bongiovanni et al., 1990). These changes were hypothesized to be due to the diminished ability of the central nervous system to activate motor neurons. Specifically, prolonged tendon vibration causes reduced Ia-afferent input, thus impairing neural activation and strength (Bongiovanni et al., 1990; Thompson and Belanger, 2002; Ushiyama et al., 2005). Although these studies used higher frequencies of vibration (100e150 Hz), it still suggests that vibration should not be applied for prolonged periods of time. The CoP data collected during this study demonstrated some intriguing results. Regardless of whether vibration was applied or not, CoP variables, on average, increased over the 2-h standing period, indicating increased movement over time. An increase in CoP range during prolonged standing is typical because it can allow the individual to mitigate some local pressure that has accumulated on the soles of the feet (Duarte and Zatsiorsky, 1999). Discomfort of the feet was the most common complaint reported amongst participants. Additionally, it has also been proposed that a general trend of increased CoP sway acts as a mechanism to decrease LBP (Lafond et al., 2009). Interestingly, those who did not experience LBP did not appear to have the same drop in CoP movement during the vibration exposure, while those who experienced LBP did.
99
When each vibration bout was examined, in general, CoP movement decreased when the vibration was applied to the low back; however this decrease was temporary and CoP movement in general actually increased over time. Since the applied vibration offered some immediate relief of pain, it is likely that participants did not have as great a need to move, thus reducing CoP movement during the vibration periods. However, once the vibration belt was turned off, CoP movement increased, corresponding to the perceived pain levels that also increased during these periods. Given the nature of the study design, it is not possible to fully discern cause and effect between pain and CoP movement, though it is hypothesized that when the vibration stimulus was removed, LBP increased, subsequently resulting in increased CoP movement to help alleviate the pain. However, it is also possible that the reduced movement observed when the vibration was applied contributed to the increase LBP reported by limiting nutrient transport into the intervertebral disc as hypothesized by Duarte and Zatsiorsky (1999). Given that those who did not report LBP did not have the same drop in CoP movement when the vibration was applied, it is possible that those individuals continued to have adequate nutrient transport and therefore did not develop LBP. Caution should be taken in applying the evidence obtained in this study to the general population. The sample used in this study (15 participants) consisted of young, healthy, asymptomatic university-aged individuals. Future research should be done with a chronic LBP population. In addition, future work examining the optimal vibration exposure (both duration and frequency of bouts) should be considered to determine if vibration can have a positive long-term effect on LBP development. In particular, it would be advantageous to examine a population who typically develops LBP during bouts of prolonged standing. Measures of perceived LBP over a similar time period as that used in the current study (2 h) as well as for longer periods of time (full work day/multiple work days) would help ascertain if vibration can effectively reduce pain in these individuals. 5. Conclusion This study demonstrated that intermittent low back vibration can offer immediate, but temporary relief of LBP. During bouts of vibration, centre of pressure movement decreased, which may have been associated with the concurrent decrease in LBP, but this did not ultimately decrease the cumulative LBP developed at the end of 2 h of standing. Therefore, based on the findings of this study, the use of vibration belts to reduce LBP development during 2 h of prolonged standing is not recommended. Acknowledgments The authors wish to acknowledge the Natural Sciences and Engineering Research Council of Canada (418655) for funding. References Aghazadeh, J., Ghaderi, M., Azghani, M., Khalkhali, H., Allahyari, T., Mohebbi, I., 2015. Anti-fatigue mats low back pain and electromyography: an interventional study. Int. J. Occup. Med. Environ. Health 28 (2), 347e356. Andersen, J.H., Haahr, J.P., Frost, P., 2007. Risk factors for more severe regional musculoskeletal symptoms: a twoyear prospective study of a general working population. Arthritis Rheum. 56 (4), 1355e1364. , F., Mannion, A.F., Pellise , F., Cedraschi, C., 2012. Non-specific low back pain. Balague Lancet 379 (9814), 482e491. Bongiovanni, L.G., Hagbarth, K.E., Stjernberg, L., 1990. Prolonged muscle vibration reducing motor output in maximal voluntary contractions in man. J. Physiol. 423, 15e26. Chen, X., Green, P.G., Levine, J.D., 2010. Neuropathic pain-like alterations in muscle nociceptor function associated with vibration-induced muscle pain. Pain 151 (2), 460e466.
100
A. Cardenas, D.E. Gregory / International Journal of Industrial Ergonomics 66 (2018) 95e100
Cochrane, D.J., 2011. Good vibrations? e the use of vibration therapy for exercise recovery, injury prevention and rehabilitation. Phys. Ther. Rev. 16 (6), 438e454. Cochrane, D.J., 2017. Effectiveness of using wearable vibration therapy to alleviate muscle soreness. Eur. J. Appl. Physiol. 11793, 501e509. Coenen, P., Parry, S., Willenberg, L., Shi, J.W., Romero, L., Blackwood, D.M., Healy, G.N., Dunstan, D.W., Straker, L.M., 2017. Associations of prolonged standing with musculoskeletal symptoms - a systematic review of laboratory studies. Gait Posture 58, 310e318. de Looze, M.P., Kuijt-Evers, L.F., van Dieen, J., 2003. Sitting comfort and discomfort and the relationships with objective measures. Ergonomics 46 (10), 985e997. Dina, O.A., Joseph, E.K., Levine, J.D., Green, P.G., 2010. Mechanisms mediating vibration-induced chronic musculoskeletal pain analyzed in the rat. J. Pain 11 (4), 369e377. Duarte, M., Zatsiorsky, V.M., 1999. Patterns of center of pressure migration during prolonged unconstrained standing. Mot. Contr. 3 (1), 12e27. Fewster, K.M., Gallagher, K.M., Callaghan, J.P., 2017. The effect of standing interventions on acute low-back postures and muscle activation patterns. Appl. Ergon. 58, 281e286. Gallagher, K., Nelson-Wong, E., Callaghan, J., 2011. Do individuals who develop transient low back pain exhibit different postural changes than non-pain developers during prolonged standing? Gait Posture 34 (4), 490e495. Garcia, J.B., Hernandez-Castro, J.J., Nunez, R.G., Pazos, M.A., Aguirre, J.O., Jreige, A., Delgado, W., Serpentegui, M., Berenguel, M., Cantemir, C., 2014. Prevalence of low back pain in Latin America: a systematic literature review. Pain Physician 17 (5), 379e391. Gregory, D.E., Callaghan, J.P., 2008. Prolonged standing as a precursor for the development of low back discomfort: an investigation of possible mechanisms. Gait Posture 28 (1), 86e92. Hagan, M., Albert, S., 1999. The clinical importance of changes in quality of life captured through the use of linear analogue scale assessment (LASA). Qual. Life Res. 8 (7), 649. €gg, O., Fritzell, P., Nordwall, A., Swedish Lumbar Spine Study Group, 2003. The Ha clinical importance of changes in outcome scores after treatment for chronic low back pain. Eur. Spine J. 12 (1), 12e20. Hoy, D., March, L., Brooks, P., Blyth, F., Woolf, A., Bain, C., Williams, G., Smith, E., Vos, T., Barendregt, J., Murray, C., Burstein, R., Buchbinder, R., 2014. The global burden of low back pain: estimates from global burden of disease. Ann. Rheum. Dis. 76 (6), 968e974. Imtiyaz, S., Veqar, Z., Shareef, M.Y., 2014. To compare the effect of vibration therapy and massage in prevention of delayed onset muscle soreness (DOMS). J. Clin. Diagn. Res. 8 (1), 133e136. Janwantanakul, P., Pensri, P., Moolkay, P., Jiamjarasrangsi, W., 2011. Development of a risk score for low back pain in office workersea cross-sectional study. BMC Muscoskel. Disord. 12 (1), 1e8. Kim, H.K., Schattschneider, J., Lee, I., Chung, K., Baron, R., Chung, J.M., 2007. Prolonged maintenance of capsaicin-induced hyperalgesia by brief daily vibration stimuli. Pain 129 (1), 93e101. Lafond, D., Champagne, A., Descarreaux, M., Dubois, J., Prado, J.M., Duarte, M., 2009. Postural control during prolonged standing n persons with chronic low back pain. Gait Posture 29 (3), 421e427. Lau, W.Y., Nosaka, K., 2011. Effect of vibration treatment on symptoms associated with eccentric exercise-induced muscle damage. Am. J. Phys. Med. Rehab. 90 (8), 648e657.
Macfarlane, G.J., Tomas, E., Papageorgiou, A.C., Croft, P.R., Jayson, M.I.V., Silman, A.J., 1997. Employment and physical work activities as predictors of future low back pain. Spine 22 (10), 1143e1149. Magee, D., Zachazewski, E., Quillen, S., 2007. Scientific Foundations and Principles of Practice in Musculoskeletal Rehabilitation, vol. 2007. St Louis Missouri: Saunders Elsevier. Melzack, R., Wall, P.D., 1965. Pain mechanisms: a new theory. Science 150 (3699), 971e978. Mohseni-Bandpei, M.A., Ahmad-Shirvani, M., Golbabaei, N., Behtash, H., ndez-de-las Pen ~ as, C., 2011. Prevalence and risk factors Shahinfar, Z., Ferna associated with low back pain in Iranian surgeons. J. Manipulative Physiol. Therapeut. 34 (6), 362e370. Nanitsos, E., Vartuli, R., Forte, A., Dennison, P., Peck, C., 2009. The effect of vibration on pain during local anesthesia injections. Aust. Dent. J. 54 (2), 94e100. Nelson-Wong, E., Callaghan, J.P., 2010a. The impact of a sloped surface on low back pain during prolonged standing work: a biomechanical analysis. Appl. Ergon. 41 (6), 787e795. Nelson-Wong, E., Callaghan, J.P., 2010b. Is muscle co-activation a predisposing factor for low back pain development during standing? A multifactorial approach for early identification of at-risk individuals. J. Electromyogr. Kinesiol. 20, 256e263. Nelson-Wong, E., Howarth, S.J., Callaghan, J.P., 2010. Acute biomechanical responses to a prolonged standing exposure in a simulated occupational setting. Ergonomics 53, 1117e1128. Perraton, L., Machotka, Z., Kumar, S., 2011. Whole-body vibration to treat low back pain: fact or fad? Physiother. Can. 63 (1), 88e93. Roelen, C.A., Schreuder, K.J., Koopmans, P.C., Groothoff, J.W., 2008. Perceived job demands relate to self-reported health complaints. Occup. Med. 58 (1), 58e63 (Oxford, England). Stewart, D.M., Gregory, D.E., 2016. The use of intermittent trunk flexion to alleviate low back pain during prolonged standing. J. Electromyogr. Kinesiol. 27, 46e51. Thompson, C., Belanger, M., 2002. Official Journal of the American College of Sports Medicine 34 (12), 2037e2044. Thorp, A.A., Owen, N., Neuhaus, M., Dunstan, D.W., 2011. Sedentary behaviors and subsequent health outcomes in adults a systematic review of longitudinal studies, 1996-2011. American Journal of Preventative Medicine 41 (2), 207e215. Tremblay, M.S., Colley, R.C., Saunders, T.J., Healy, G.N., Owen, N., 2010. Physiological and health implications of a sedentary lifestyle. Appl. Physiol. Nutr. Metabol. 35 (6), 725e740. Ushiyama, J., Masani, K., Kouzaki, M., Kanehisa, H., Fukunaga, T., 2005. Difference in aftereffects following prolonged Achilles tendon vibration on muscle activity during maximal voluntary contraction among plantar flexor synergists. J. Appl. Physiol. 98 (4), 1427e1433. , M.C., 1999. The influence of occupation on lumbar degeneration. Videman, T., Battie Spine 24 (11), 1164e1168. Waters, T.R., Dick, R.B., 2015. Evidence of health risks associated with prolonged standing at work and intervention effectiveness. Rehabil. Nurs. 40 (3), 148e165. Womersley, L., May, S., 2006. Sitting posture of subjects with postural backache. J. Manipulative Physiol. Therapeut. 29 (3), 213e218. Xu, Y., Back, E., Orhede, E., 1997. Work environment and low back pain: the influence of occupational activities. Occup. Environ. Med. 54 (10), 741. Zafar, H., Alghadir, A., Anwer, S., Al-Eisa, E., 2015. Therapeutic effects of whole-body vibration training in knee osteoarthritis: a systematic review and meta-analysis. Arch. Phys. Med. Rehabil. 96 (8), 1525e1532.
Contents lists available at ScienceDirect
International Journal of Industrial Ergonomics journal homepage: www.elsevier.com/locate/ergon
Can cutaneous vibration affect pain development? Testing the efficacy of a vibrating belt applied intermittently to the low back region during prolonged standing Analyssa Cardenas a, Diane E. Gregory b, * a b
Department of Kinesiology, University of Waterloo, Waterloo, Canada Department of Kinesiology & Physical Education/Health Sciences, Wilfrid Laurier University, Waterloo, Canada
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 July 2017 Received in revised form 11 January 2018 Accepted 23 January 2018
Standing-induced low back pain (LBP) is becoming more common in the workplace and has been shown to develop in periods of as short as 2 h. The purpose of this study was to determine if vibration, an increasingly popular method of pain relief, applied intermittently (every 15 min) directly to the low back could alleviate pain developed during a 2-h period of standing. Two separate collection days were conducted (order randomized). During the control day, no vibration was applied during the 2 h of standing; on an experimental day, vibration was applied via a vibration belt in 3-min durations every 15 min for 2 h. During both data collections, perceived LBP was collected via a visual analogue scale every 15 min; on the experimental day LBP was collected just prior to and following each vibration bout. Force plate data were also collected to determine centre of pressure changed over time. LBP significantly increased over time on both collection days; however, on the vibration day LBP reported just prior to each vibration bout was significantly higher than that immediately following, suggesting a temporary relief of pain. However, this relief of pain was not sustained as the level of perceived LBP at the end of the 2 h on the control day was not significantly different from that on the vibration day. Decreases in anterior-posterior and medial-lateral centre of pressure movement were also observed during each bout of vibration compared to during the control day. In conclusion, while intermittent vibration applied to the low back appears to relieve LBP developed during standing, this relief is temporary. © 2018 Published by Elsevier B.V.
Keywords: Vibration Massage belt Centre of pressure Visual analogue scale Low back pain
1. Introduction Low back pain (LBP) continues to be a prevalent cause of missed work and disability among the developed world (Hoy et al., 2014; et al., 2012). Typically, manual material handing is thought Balague to be the major contributor of work-related LBP; however recent evidence has shown that sedentary tasks can have negative health impacts (Thorp et al., 2011; Tremblay et al., 2010) and can result in LBP in the case of prolonged sitting (Garcia et al., 2014; Womersley , 1999) and standing (Coenen & May 2006; Videman and Battie et al., 2017; Waters and Dick, 2015; Janwantanakul et al., 2011; Mohseni-Bandpei et al., 2011; Nelson-Wong and Callaghan, 2010a; Gregory and Callaghan, 2008; Andersen et al., 2007; Roelen et al.,
* Corresponding author. Department of Kinesiology & Physical Education, Department of Health Sciences, Wilfrid Laurier University, 75 University Ave West, Waterloo, Ontario, N2L 3C5, Canada. E-mail address: [email protected] (D.E. Gregory). https://doi.org/10.1016/j.ergon.2018.01.015 0169-8141/© 2018 Published by Elsevier B.V.
2008). While a significant number of ergonomic interventions, primarily related to chair design, have been developed and examined for sitting, less focus has been placed on prolonged standing. The efficacy of a variety of ergonomic interventions including floor type and mats (Aghazadeh et al., 2015; Waters and Dick, 2015), intermittent spinal flexion (Stewart and Gregory, 2016), and standing on a sloped surface (Fewster et al., 2017; Nelson-Wong and Callaghan, 2010a) have been examined, however LBP still remains prevalent, suggesting a need for alternative pain mitigation strategies. Recently, vibration, administered through whole body vibration (typically by standing on a vibrating platform; Perraton et al., 2011) or through the use of a massage device (Imtiyaz et al., 2014), has become more common for musculoskeletal pain management (Cochrane, 2017; Zafar et al., 2015; Lau and Nosaka, 2011). One possible hypothesis is that vibration inhibits nerve fibres responsible for transmitting pain (Magee et al., 2007). This hypothesis, termed the gate control theory of pain (Melzack and Wall, 1965),
96
A. Cardenas, D.E. Gregory / International Journal of Industrial Ergonomics 66 (2018) 95e100
suggests that vibration stimulates the same large diameter peripheral nerve fibres that are activated in response to pain (Melzack and Wall, 1965; Cochrane, 2011; Nanitsos et al., 2009), thereby preventing transmission of pain-related information. Since prolonged standing has been shown to result in significant levels of LBP in previously asymptomatic populations after as little as 2 h (Stewart and Gregory, 2016; Nelson-Wong and Callaghan, 2010b; Nelson-Wong et al., 2010; Gregory and Callaghan, 2008), it is possible that exposure to low back vibration may help alleviate or reduce LBP in such individuals, providing an alternative mechanism of pain relief. Further, given the increased popularity of sit-stand workstations, the prevalence of prolonged standing is also increasing among many occupations. Therefore, the primary purpose of this study was to determine if intermittent bouts of vibration applied to the low back region through a vibrating massage belt is effective at reducing the level of LBP developed during a 2-h period of standing. The secondary purpose of this study was to determine if vibration alters movement of the centre of pressure (CoP) at the feet during prolonged standing. It was hypothesized that 1) vibration would significantly reduce LBP developed during prolonged standing, and 2) vibration would significantly reduce CoP movement at the feet. 2. Methods
vibration periods). The order of the control and experimental days were randomized and each collection was completed at approximately the same time of day one week apart.
2.3. Data collection Ratings of each of perceived LBP, leg/feet pain, and overall pain were recorded using 100 mm visual analogue scales (VAS) with the anchors of no pain (0 mm) and worst pain imaginable (100 mm). On the control day, ratings of perceived LBP were collected every 15 min during the 2-h standing protocol. On the experimental day, two ratings of perceived LBP were collected every 15 min; one just prior to the start of the 3-min vibration and one immediately following the vibration for a total of 16 ratings (Fig. 1). Participants also had the opportunity, if they wished, to indicate on the same form if they were feeling any of the following pain-related symptoms in their backs: tiredness, soreness, numbness, sharp, dull, tingling, distributed, and localized (de Looze et al., 2003). Force plate data were recorded on both the control and experimental collection days. On the control day, 3-min periods were recorded just prior to each pain rating. On the experimental day, 3min periods were recorded just prior to each vibration application (VibOFF) and during each 3-min vibration period (VibON); Fig. 1. Force plate data were sampled at 128 Hz.
2.1. Participants A sample of 15 healthy participants (8 female; 7 male) were recruited from a university population (mean (standard deviation) age ¼ 21 years (1.0); height ¼ 1.67 m (0.09); mass ¼ 62.6 kg (9.6)). Participants were required to be free of LPB for the previous 12 months and not have suffered from any neurological conditions that could affect balance. Participants were asked to come to the laboratory for testing on two separate days, one week apart, to perform a 2-h standing protocol. 2.2. Study protocol On the first visit, participants were briefed on the study protocol, given the opportunity to familiarize themselves with the vibration belt device, and asked to review and sign a consent form for the study which had been approved by the University human ethics board. Participants were then instructed to stand for a 2 h period (on a 60 90 cm force plate; Bertec, Columbus, Ohio) while performing tasks resembling jobs that often require prolonged periods of standing: small object assembly, currency sorting, barcode scanning, and typing (each performed for 30 min). The desk on which these tasks were performed was set for each participant such that the elbow angle was slightly greater than 90 when the forearms rested on the table. This desk height was the same on both collection days. Leaning on the desk was not permitted, but the forearms were allowed to rest while performing the tasks. Further, individuals were instructed to keep their feet on the force plate but they could shift their weight and/or move their feet within the area of the force plate throughout the collection. Personal athletic footwear was worn by each participant. Prior to both collection periods, each participant was fitted with a vibrating massage belt (Zewa Spa Buddy; factory setting vibration ¼ 53 Hz) around his/her waist such that the vibration was applied to the lower back and sacrum region. On the control day, the belt was worn for the entire duration of the study, but it was turned off the entire time; on the experimental day, vibration was applied via the belt for 3-min durations every 15 min (total of 8
2.4. Data analysis Perceived pain was quantified by measuring the distance from the origin (0 mm) to the participant's mark on the 100 mm VAS; the greater the distance measured, the more intense the pain. Participants were subsequently classified as either LBP developers (reached a low back VAS score of at least 10 mm at any point during the control day standing period) or non-low back pain developers (never reached 10 mm during the control day standing period), as 10 mm has been previously considered a clinically significant level of LBP (Gallagher et al., 2011; Nelson-Wong and Callaghan, 2010a; Hagan and Albert, 1999). Force plate data were low-pass filtered at 6 Hz using a second order dual-pass Butterworth filter and CoP at the feet was determined. Variables of interest, which were determined for each 3min force plate collection period, included anterior-posterior (AP) CoP range (CoPAP), medio-lateral (ML) CoP range (CoPML), AP root mean square (RMS) (CoPAP_RMS), ML RMS (CoPML_RMS), AP velocity range (VelocityAP), ML velocity range (VelocityML), AP velocity RMS (VelocityAP_RMS), ML velocity RMS (VelocityML_RMS), and cumulative path length (CPL).
2.5. Statistical analysis Three-way analysis of variance (ANOVA) tests and Tukey posthoc tests (Statistical Analysis System (SAS) software) were used to examine the effect of vibration exposure (2 levels: control/experimental day (pre-vibration time points)), time point (8 levels; 15 min intervals; the pre vibration VAS scores on the experimental day were compared with the 15 min interval scores on the control day), and LBP classification (2 levels: yes/no) on VAS scores. A separate three-way ANOVA was conducted on only the experimental day data with the following factors: pre/post vibration, time point, and LBP classification on VAS scores. Similar three-way ANOVA statistical analyses were conducted on the aforementioned CoP variables. An alpha level of 0.05 was set as significant.
A. Cardenas, D.E. Gregory / International Journal of Industrial Ergonomics 66 (2018) 95e100
97
Fig. 1. Control and experimental day protocol timeline. Time is shown in 15 min intervals over the 2-h collection. Solid grey regions indicate when force plate data were collected to calculate CoP changes and diagonal line regions indicate when vibration was applied. All regions represent 3 min of time. Solid black vertical lines indicate when VAS pain ratings were recorded.
3. Results 3.1. Perceived pain Of the 15 participants, seven were classified as LBP developers (average (standard error) VAS of 26.3 mm (4.6) at the 2-h mark) and eight were classified as non-LBP developers (average VAS of 2.3 mm (0.9) at the 2-h mark). 3.1.1. Perceived pain over time On both the control day and the experimental day, ratings of perceived pain in the low back (p ¼ 0.0001), feet and legs (p ¼ 0.0001) and overall pain (p ¼ 0.0001) increased over time (Fig. 2). Further, in addition to greater LBP, those who were classified as LBP developers reported more feet/leg and overall pain compared to non-LBP developers as indicated by significant interactions between classification and time point (p ¼ 0.009 for feet/ legs and p ¼ 0.002 for overall pain). 3.1.2. Perceived pain developed on control day versus experimental day and pre versus post vibration Collapsed across time point and LBP classification, no differences in perceived pain were observed between the control day and the vibration day (specifically at time points just before each vibration exposure) (p ¼ 0.69, 0.50, 0.31 for low back, legs/feet, and overall pain, respectively). However, on the experimental day, collapsed across time and LBP classification, significant differences in perceived LBP were
observed immediately prior to and immediately after each 3-min bout of vibration exposure (p ¼ 0.039). Specifically, average LBP before vibration exposure was 9.11 mm (3.42) and 7.56 mm (2.99) immediately after. At the 75 and 90-min marks, the vibration exposure, on average, reduced perceived LBP from an above clinical level (>10 mm) to below (Fig. 3); however this sub-clinical level of LBP did not continue for the remainder of the 2 h. Further, this decrease was not different over time as no interaction with time point was observed (p ¼ 0.20). No main effect of vibration exposure was observed for perceived pain in the feet/legs (p ¼ 0.66) or in overall pain (p ¼ 0.20). A significant interaction between pre/post vibration and time point was observed for pain in the feet/legs (p ¼ 0.028; Fig. 4) such that at the 75 and 105 min marks, post vibration perceived pain was actually higher than pre vibration (Fig. 4). 3.2. Centre of pressure (CoP) 3.2.1. CoP over time Regardless of vibration exposure (i.e. control versus experimental day), a number of CoP variables were significantly affected by time such that, in general, CoP variables tended to increase, albeit minimally, over time (Fig. 5). Specifically, the following variables were affected by time point: range in the CoPAP (p ¼ 0.023), range in CoPML (p ¼ 0.012), CoPAP_RMS (p ¼ 0.003), CoPML_RMS (p ¼ 0.0007), and CPL (p ¼ 0.026). One additional variable (range of the CoPML velocity) was not affected by time as a main effect; however a significant interaction between time point and vibration exposure was observed (p ¼ 0.023) such that VelocityML tended to vary substantially over time on both the control day and the experimental day.
20 18
Low Back Pain (mm)
16 14 12
10
Pre
8
Post
6
Control
4 2 0
Fig. 2. Average (standard error) ratings of perceived low back, feet/legs, and overall pain over time collapsed across day (control and experimental) and LBP classification. Bars within the same category (i.e. LBP; feet/legs; overall) with the same letter are not significantly different from one another (p > 0.05). For example, for the black bars, which represent overall pain, the magnitude at 15 min is not significantly different from the magnitude at 30 or 45 min as all 3 bars have at least one common letter above (in this case “A”). However, at 60 min, there is no “A” above the black overall pain bar, and therefore it is significantly different from 15 min, but not different from 30 or 45 min because each bar shares the letter “B”.
15
30
45
60
75
90
105
120
Time (mins) Fig. 3. Average (standard error) ratings of perceived low back pain on the control day as well as pre and post vibration exposure on the experimental day (data collapsed across LBP classification). Collapsed across time, Pre versus Post LBP levels were significantly different (p ¼ 0.039); no significant interaction between pre/post and time was observed. Effect of time point indicated previously in Fig. 2. No significant difference between the pre vibration LBP scores and the control day LBP scores.
A. Cardenas, D.E. Gregory / International Journal of Industrial Ergonomics 66 (2018) 95e100
a
35
Feet/Leg Pain (mm)
30 25
*
*
20
0.05 Pre
15
Post
10 5 0 15
30
45
60
75
*
0.04
90
105
120
COPML_RMS (m)
98
0.03 0.02 0.01 0
Time (mm)
Control
VibOFF
VibON
b 6
Cumulative Path Length (m)
Fig. 4. Average (standard error) perceived feet/leg pain over time on the experimental day (collapsed across LBP classification). Effect of time point indicated previously in Fig. 2. Significant interaction between time point and pre/post (p ¼ 0.028); asterisks indicate time point where post vibration feet/leg pain scores were higher than pre vibration.
5
Non-LBP developers
*
LBP developers
4 3 2 1 0 Control
Fig. 5. Average (standard error) CoP variables significantly affected by time. For CoPAP, 15- and 30-min differed from 105-min (p ¼ 0.023); for CoPML, 15-min differed from 90min (p ¼ 0.012); for CoPAP_RMS, 15-, 30-, and 45-min differed from 105-min (p ¼ 0.003); for CoPML_RMS, 15-min differed from 75-, 90-, and 105-min; 30-min also differed from 75-min (p ¼ 0.0007); for CPL, 60-min differed from 90-min (p ¼ 0.026). Data collapsed across day (control and experimental) and LBP classification..
3.2.2. CoP during control day versus prior to and immediately following vibration on experimental day In terms of the effect of vibration exposure, two variables (CoPML_RMS and CPL) were significantly affected (Fig. 6). In general, these CoP variables tended to be highest on the control day and lowest on the experimental day when the vibration was on. For CoPML_RMS (p ¼ 0.04), the control day only significantly differed from vibration ON condition. For the CPL, the control day significantly differed from both the vibration ON and vibration OFF conditions (Fig. 6a; p ¼ 0.001). However, only those who were non LBPdevelopers actually showed the drop in CPL on the experimental day; the CPL of the LBP developers did not differ between the control day and the experimental day (indicated by significant interaction between LBP classification and vibration exposure; p ¼ 0.032; Fig. 6b). No other main effects of LBP classification were observed. 4. Discussion Low back pain (LBP) has long been recognized as a significant health issue, particularly in occupations that require prolonged periods of standing (Macfarlane et al., 1997; Xu et al., 1997). With the increase in LBP prevalence in many occupations, there has been a growing interest in the use of vibration, which has been shown to be effective at reducing muscle pain (Cochrane, 2017; Zafar et al., 2015; Lau and Nosaka, 2011). This study demonstrated that low back vibration can offer an immediate relief of LBP over a short period of time, but does not appear to offer long term (over 2 h) positive effects.
VibOFF
VibON
Fig. 6. (a) Average (standard error) CoPML_RMS on the control day and on the experimental day (vibration on and vibration off); collapsed across time point and LBP classification. Only the control and VibON conditions significantly differed from one another (indicated by asterisk). (b) Average (standard error) CPL on the control and experimental day (including when vibration was on and off) for those who developed LBP and those who did not; collapsed across time point. Note that the CPL did not differ between the LBP and non-LBP developers during the VibOFF and VibON conditions, but that on the control day, the CPL was significantly higher for the non-LBP developers compared to non-LBP developers (indicated by asterisk).
Specifically, after 3 min of low back vibration, an immediate relief in LBP was observed. However, this decrease in reported pain was transient because once the vibration was removed, the pain returned by the time the next vibration period was applied (12 min later). Further, LBP reported at the 2-h mark was no different on the experimental day when vibration was applied compared to the control day despite the observed immediate drops in pain reported after each vibration bout, indicating that the temporary relief was not effective at mitigating pain longer term. The observed transient and immediate relief of pain following each bout of vibration can most likely be explained by the gate control theory of pain (Melzack and Wall, 1965). The brain receives information on painful stimuli through the noxious stimulus itself, the modulation of peripheral nerves, and the descending contrl by the central nervous system (Melzack and Wall, 1965). The injury detection threshold of large diameter peripheral nerve fibres (Ab fibres) increases when the nerves are stimulated (Melzack and Wall, 1965). When vibration is applied, the activation of low threshold mechanoreceptors causes the stimulation of these large diameter peripheral nerves (Melzack and Wall, 1965; Cochrane, 2011; Nanitsos et al., 2009). This effectively induces inhibition of the perception of pain by blocking the transmission of information being sent to the central nervous system (Melzack and Wall, 1965). Although the 3 min bouts of low back vibration caused an immediate decrease in pain for a short period of time, it did not eliminate the LBP completely. Average LBP prior to vibration
A. Cardenas, D.E. Gregory / International Journal of Industrial Ergonomics 66 (2018) 95e100
exposure was 9.11 mm and reduced to 7.56 mm immediately following vibration. Interestingly, at the 75 and 90-min mark, of the standing protocol, vibration temporarily reduced LBP to a below clinical level (<10 mm; Gallagher et al., 2011; Nelson-Wong and Callaghan, 2010a; Hagan and Albert, 1999). However, by the 2-h mark, there was no difference in low back pain between the experimental (vibration) day and the control day, indicating that vibration is not effective at long-term pain reduction. It should be noted that, although a significant drop in pain was noted, this drop was only ~2 mm which may not enough to have a notable impact on the individual. Previous research has suggested that a drop in pain €gg et al., 2003). must be at least 8 mm to be considered effective (Ha However, there were two individuals in the study that did report a greater than 8 mm drop in LBP following vibration, suggesting that it may be an effective strategy for some. Though, for both of these individuals, their LBP score at the end of the control day and the vibration day only differed by 1 mm, suggesting that although pain relief was observed immediately following vibration, it was not sustained. Although the vibration offered temporary relief of pain, there is also the possibility of detrimental effects on a long term scale. It is speculated that this vibration, if applied for a longer period of time, may trigger an exaggerated pain response. It has been demonstrated that mechanical vibration of a similar frequency to that in the current study (60e80 Hz) applied to the hind limb of rat resulted in skeletal muscle hyperalgesia (Dina et al., 2010). This hypersensitivity to pain can be explained by a number of different mechanisms. When mechanical vibration is applied, very highfiring nociceptors produce an enhanced and prolonged response to sustained mechanical stimulation (Chen et al., 2010). The vibration lowers the mechanical threshold, suggesting that these nociceptors may contribute to neuropathic muscle pain even after vibration is removed (Chen et al., 2010). Repeated daily applications of brief vibration stimulation have also been shown to prolong hyperalgesia in comparison to no vibration exposure (Kim et al., 2007). Further research needs to be conducted to determine whether repeated intermittent vibration over time will induce a higher sensitivity of pain in the lower back. In addition to increased pain sensitively, prolonged vibration exposure may also disrupt motor control patterns. The use of muscle vibration for prolonged periods of time has been shown to cause a reduction in electrical activity of muscles, motor unit firing rates, and contraction force for both intermittent and sustained maximal voluntary contractions (Bongiovanni et al., 1990). These changes were hypothesized to be due to the diminished ability of the central nervous system to activate motor neurons. Specifically, prolonged tendon vibration causes reduced Ia-afferent input, thus impairing neural activation and strength (Bongiovanni et al., 1990; Thompson and Belanger, 2002; Ushiyama et al., 2005). Although these studies used higher frequencies of vibration (100e150 Hz), it still suggests that vibration should not be applied for prolonged periods of time. The CoP data collected during this study demonstrated some intriguing results. Regardless of whether vibration was applied or not, CoP variables, on average, increased over the 2-h standing period, indicating increased movement over time. An increase in CoP range during prolonged standing is typical because it can allow the individual to mitigate some local pressure that has accumulated on the soles of the feet (Duarte and Zatsiorsky, 1999). Discomfort of the feet was the most common complaint reported amongst participants. Additionally, it has also been proposed that a general trend of increased CoP sway acts as a mechanism to decrease LBP (Lafond et al., 2009). Interestingly, those who did not experience LBP did not appear to have the same drop in CoP movement during the vibration exposure, while those who experienced LBP did.
99
When each vibration bout was examined, in general, CoP movement decreased when the vibration was applied to the low back; however this decrease was temporary and CoP movement in general actually increased over time. Since the applied vibration offered some immediate relief of pain, it is likely that participants did not have as great a need to move, thus reducing CoP movement during the vibration periods. However, once the vibration belt was turned off, CoP movement increased, corresponding to the perceived pain levels that also increased during these periods. Given the nature of the study design, it is not possible to fully discern cause and effect between pain and CoP movement, though it is hypothesized that when the vibration stimulus was removed, LBP increased, subsequently resulting in increased CoP movement to help alleviate the pain. However, it is also possible that the reduced movement observed when the vibration was applied contributed to the increase LBP reported by limiting nutrient transport into the intervertebral disc as hypothesized by Duarte and Zatsiorsky (1999). Given that those who did not report LBP did not have the same drop in CoP movement when the vibration was applied, it is possible that those individuals continued to have adequate nutrient transport and therefore did not develop LBP. Caution should be taken in applying the evidence obtained in this study to the general population. The sample used in this study (15 participants) consisted of young, healthy, asymptomatic university-aged individuals. Future research should be done with a chronic LBP population. In addition, future work examining the optimal vibration exposure (both duration and frequency of bouts) should be considered to determine if vibration can have a positive long-term effect on LBP development. In particular, it would be advantageous to examine a population who typically develops LBP during bouts of prolonged standing. Measures of perceived LBP over a similar time period as that used in the current study (2 h) as well as for longer periods of time (full work day/multiple work days) would help ascertain if vibration can effectively reduce pain in these individuals. 5. Conclusion This study demonstrated that intermittent low back vibration can offer immediate, but temporary relief of LBP. During bouts of vibration, centre of pressure movement decreased, which may have been associated with the concurrent decrease in LBP, but this did not ultimately decrease the cumulative LBP developed at the end of 2 h of standing. Therefore, based on the findings of this study, the use of vibration belts to reduce LBP development during 2 h of prolonged standing is not recommended. Acknowledgments The authors wish to acknowledge the Natural Sciences and Engineering Research Council of Canada (418655) for funding. References Aghazadeh, J., Ghaderi, M., Azghani, M., Khalkhali, H., Allahyari, T., Mohebbi, I., 2015. Anti-fatigue mats low back pain and electromyography: an interventional study. Int. J. Occup. Med. Environ. Health 28 (2), 347e356. Andersen, J.H., Haahr, J.P., Frost, P., 2007. Risk factors for more severe regional musculoskeletal symptoms: a twoyear prospective study of a general working population. Arthritis Rheum. 56 (4), 1355e1364. , F., Mannion, A.F., Pellise , F., Cedraschi, C., 2012. Non-specific low back pain. Balague Lancet 379 (9814), 482e491. Bongiovanni, L.G., Hagbarth, K.E., Stjernberg, L., 1990. Prolonged muscle vibration reducing motor output in maximal voluntary contractions in man. J. Physiol. 423, 15e26. Chen, X., Green, P.G., Levine, J.D., 2010. Neuropathic pain-like alterations in muscle nociceptor function associated with vibration-induced muscle pain. Pain 151 (2), 460e466.
100
A. Cardenas, D.E. Gregory / International Journal of Industrial Ergonomics 66 (2018) 95e100
Cochrane, D.J., 2011. Good vibrations? e the use of vibration therapy for exercise recovery, injury prevention and rehabilitation. Phys. Ther. Rev. 16 (6), 438e454. Cochrane, D.J., 2017. Effectiveness of using wearable vibration therapy to alleviate muscle soreness. Eur. J. Appl. Physiol. 11793, 501e509. Coenen, P., Parry, S., Willenberg, L., Shi, J.W., Romero, L., Blackwood, D.M., Healy, G.N., Dunstan, D.W., Straker, L.M., 2017. Associations of prolonged standing with musculoskeletal symptoms - a systematic review of laboratory studies. Gait Posture 58, 310e318. de Looze, M.P., Kuijt-Evers, L.F., van Dieen, J., 2003. Sitting comfort and discomfort and the relationships with objective measures. Ergonomics 46 (10), 985e997. Dina, O.A., Joseph, E.K., Levine, J.D., Green, P.G., 2010. Mechanisms mediating vibration-induced chronic musculoskeletal pain analyzed in the rat. J. Pain 11 (4), 369e377. Duarte, M., Zatsiorsky, V.M., 1999. Patterns of center of pressure migration during prolonged unconstrained standing. Mot. Contr. 3 (1), 12e27. Fewster, K.M., Gallagher, K.M., Callaghan, J.P., 2017. The effect of standing interventions on acute low-back postures and muscle activation patterns. Appl. Ergon. 58, 281e286. Gallagher, K., Nelson-Wong, E., Callaghan, J., 2011. Do individuals who develop transient low back pain exhibit different postural changes than non-pain developers during prolonged standing? Gait Posture 34 (4), 490e495. Garcia, J.B., Hernandez-Castro, J.J., Nunez, R.G., Pazos, M.A., Aguirre, J.O., Jreige, A., Delgado, W., Serpentegui, M., Berenguel, M., Cantemir, C., 2014. Prevalence of low back pain in Latin America: a systematic literature review. Pain Physician 17 (5), 379e391. Gregory, D.E., Callaghan, J.P., 2008. Prolonged standing as a precursor for the development of low back discomfort: an investigation of possible mechanisms. Gait Posture 28 (1), 86e92. Hagan, M., Albert, S., 1999. The clinical importance of changes in quality of life captured through the use of linear analogue scale assessment (LASA). Qual. Life Res. 8 (7), 649. €gg, O., Fritzell, P., Nordwall, A., Swedish Lumbar Spine Study Group, 2003. The Ha clinical importance of changes in outcome scores after treatment for chronic low back pain. Eur. Spine J. 12 (1), 12e20. Hoy, D., March, L., Brooks, P., Blyth, F., Woolf, A., Bain, C., Williams, G., Smith, E., Vos, T., Barendregt, J., Murray, C., Burstein, R., Buchbinder, R., 2014. The global burden of low back pain: estimates from global burden of disease. Ann. Rheum. Dis. 76 (6), 968e974. Imtiyaz, S., Veqar, Z., Shareef, M.Y., 2014. To compare the effect of vibration therapy and massage in prevention of delayed onset muscle soreness (DOMS). J. Clin. Diagn. Res. 8 (1), 133e136. Janwantanakul, P., Pensri, P., Moolkay, P., Jiamjarasrangsi, W., 2011. Development of a risk score for low back pain in office workersea cross-sectional study. BMC Muscoskel. Disord. 12 (1), 1e8. Kim, H.K., Schattschneider, J., Lee, I., Chung, K., Baron, R., Chung, J.M., 2007. Prolonged maintenance of capsaicin-induced hyperalgesia by brief daily vibration stimuli. Pain 129 (1), 93e101. Lafond, D., Champagne, A., Descarreaux, M., Dubois, J., Prado, J.M., Duarte, M., 2009. Postural control during prolonged standing n persons with chronic low back pain. Gait Posture 29 (3), 421e427. Lau, W.Y., Nosaka, K., 2011. Effect of vibration treatment on symptoms associated with eccentric exercise-induced muscle damage. Am. J. Phys. Med. Rehab. 90 (8), 648e657.
Macfarlane, G.J., Tomas, E., Papageorgiou, A.C., Croft, P.R., Jayson, M.I.V., Silman, A.J., 1997. Employment and physical work activities as predictors of future low back pain. Spine 22 (10), 1143e1149. Magee, D., Zachazewski, E., Quillen, S., 2007. Scientific Foundations and Principles of Practice in Musculoskeletal Rehabilitation, vol. 2007. St Louis Missouri: Saunders Elsevier. Melzack, R., Wall, P.D., 1965. Pain mechanisms: a new theory. Science 150 (3699), 971e978. Mohseni-Bandpei, M.A., Ahmad-Shirvani, M., Golbabaei, N., Behtash, H., ndez-de-las Pen ~ as, C., 2011. Prevalence and risk factors Shahinfar, Z., Ferna associated with low back pain in Iranian surgeons. J. Manipulative Physiol. Therapeut. 34 (6), 362e370. Nanitsos, E., Vartuli, R., Forte, A., Dennison, P., Peck, C., 2009. The effect of vibration on pain during local anesthesia injections. Aust. Dent. J. 54 (2), 94e100. Nelson-Wong, E., Callaghan, J.P., 2010a. The impact of a sloped surface on low back pain during prolonged standing work: a biomechanical analysis. Appl. Ergon. 41 (6), 787e795. Nelson-Wong, E., Callaghan, J.P., 2010b. Is muscle co-activation a predisposing factor for low back pain development during standing? A multifactorial approach for early identification of at-risk individuals. J. Electromyogr. Kinesiol. 20, 256e263. Nelson-Wong, E., Howarth, S.J., Callaghan, J.P., 2010. Acute biomechanical responses to a prolonged standing exposure in a simulated occupational setting. Ergonomics 53, 1117e1128. Perraton, L., Machotka, Z., Kumar, S., 2011. Whole-body vibration to treat low back pain: fact or fad? Physiother. Can. 63 (1), 88e93. Roelen, C.A., Schreuder, K.J., Koopmans, P.C., Groothoff, J.W., 2008. Perceived job demands relate to self-reported health complaints. Occup. Med. 58 (1), 58e63 (Oxford, England). Stewart, D.M., Gregory, D.E., 2016. The use of intermittent trunk flexion to alleviate low back pain during prolonged standing. J. Electromyogr. Kinesiol. 27, 46e51. Thompson, C., Belanger, M., 2002. Official Journal of the American College of Sports Medicine 34 (12), 2037e2044. Thorp, A.A., Owen, N., Neuhaus, M., Dunstan, D.W., 2011. Sedentary behaviors and subsequent health outcomes in adults a systematic review of longitudinal studies, 1996-2011. American Journal of Preventative Medicine 41 (2), 207e215. Tremblay, M.S., Colley, R.C., Saunders, T.J., Healy, G.N., Owen, N., 2010. Physiological and health implications of a sedentary lifestyle. Appl. Physiol. Nutr. Metabol. 35 (6), 725e740. Ushiyama, J., Masani, K., Kouzaki, M., Kanehisa, H., Fukunaga, T., 2005. Difference in aftereffects following prolonged Achilles tendon vibration on muscle activity during maximal voluntary contraction among plantar flexor synergists. J. Appl. Physiol. 98 (4), 1427e1433. , M.C., 1999. The influence of occupation on lumbar degeneration. Videman, T., Battie Spine 24 (11), 1164e1168. Waters, T.R., Dick, R.B., 2015. Evidence of health risks associated with prolonged standing at work and intervention effectiveness. Rehabil. Nurs. 40 (3), 148e165. Womersley, L., May, S., 2006. Sitting posture of subjects with postural backache. J. Manipulative Physiol. Therapeut. 29 (3), 213e218. Xu, Y., Back, E., Orhede, E., 1997. Work environment and low back pain: the influence of occupational activities. Occup. Environ. Med. 54 (10), 741. Zafar, H., Alghadir, A., Anwer, S., Al-Eisa, E., 2015. Therapeutic effects of whole-body vibration training in knee osteoarthritis: a systematic review and meta-analysis. Arch. Phys. Med. Rehabil. 96 (8), 1525e1532.